Implement top controls show/hide functionality for main thread scrolling

public/platform/WebTopControlsState.h

Index: public/platform/WebTopControlsState.h
diff --git a/public/platform/WebImageGenerator.h b/public/platform/WebTopControlsState.h
similarity index 82%
copy from public/platform/WebImageGenerator.h
copy to public/platform/WebTopControlsState.h
index bb17f4d6df96a2dcc73efa069d2c6646a2338ab9..b67820222e80ab4a63fc7c58fb20560e917de0f6 100644
--- a/public/platform/WebImageGenerator.h
+++ b/public/platform/WebTopControlsState.h
@@ -28,21 +28,19 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef WebImageGenerator_h
-#define WebImageGenerator_h
-
-#include "WebCommon.h"
-
-class SkData;
-class SkImageGenerator;
+#ifndef WebTopControlsState_h
+#define WebTopControlsState_h
 
 namespace blink {
 
-class BLINK_EXPORT WebImageGenerator {
-public:
-    static SkImageGenerator* create(SkData*);
+// Represents Top Controls State. Values should be equivalent to
+// Chromium and CC versions namely: |content::TopControlsState|, and
+// |cc::TopControlsState|
+enum WebTopControlsState {
+    WebTopControlsShown = 1,
+    WebTopControlsHidden = 2,
+    WebTopControlsBoth = 3
 };
 
 } // namespace blink
-
 #endif